V.A. Menon and V.R. Ragade
Abstract
The widespread use of chlorpyrifos in agricultural systems increases the mortality risk for non-target aquatic organisms. The objective of the study was to evaluate the median lethal concentration (LC50) of commercial-grade chlorpyrifos EC 20% on the freshwater fish, Oreochromis mossambicus. Acute toxicity tests were conducted over a 96-hour period using a static system as per the OECD Test guidelines across a series of concentrations. The concentration-mortality data were subjected to Probit regression analysis to determine the LC50. The Probit model exhibited an excellent fit to the data (96 h ?2 = 1.182, df = 3, p > 0.05), validating its application. The 96-hour LC50 was determined to be 0.296 ?g l?¹ (95% CI: 0.263- 0.326). The steep Probit slope indicated a highly consistent physiological tolerance across the fish population used in the experiment. Based on the findings of the study, chlorpyrifos is classified as sensitive to O. mossambicus.